Lissoclinotoxins E and F, novel cytotoxic alkaloids from a Philippine didemnid ascidian

Bioassay-guided fractionation of the MeOH extract from a Philippine didemnid ascidian resulted in the isolation of two new dimeric alkaloids, lissoclinotoxins E () and F (). The polysulfide structures for compounds and were determined by interpretation of spectroscopic data and chemical degradation. Computational chemistry studies suggested that the N-alkyl chains about the tricyclic systems of lissoclinotoxins E and F had trans and cis orientations, respectively. Alkaloids and displayed IC50 values of 2.3 and 1.5 μg/mL, respectively, towards the PTEN-deficient human breast carcinoma cell line, MDA-MB-468.